Effect of phosphorus and iron on grain sorghum

Abstract

Iron deficiency in grain sorghum (Sorghum bicolor (L.) Moench) is a major problem in many soils in the Western Great Plains. Yield response to applied iron and other micronutrients is not always predictable due to the many complex interactions that exist among micronutrients and specifically with P and Fe. Any information gained will help solve the enigma surrounding the complexity of these reactions and will eventually lead to practical solutions of Fe deficiency problems.

The objectives of this study were to determine the effect of P and Fe applied singly and in combination with other micronutrients on (a) yield and micronutrient concentration of grain sorghum and (b) DTPA extractable Fe.

Two soils (Quinlan clay loam ‐ Typic Ustocrept and Spur silt loam ‐ Fluventic Haplustoll) that were deficient in P and Fe were collected from Western Oklahoma for a greenhouse experiment. Soils were kept field moist, mixed thoroughly and placed in pots. Nitrogen, P as ammonium polyphosphate, and micronutrients were applied and soils were cropped to grain sorghum. Two harvests were obtained and dry matter yield, plant composition and effects of P on extractable micronutrients were determined.

Effect of P plus micronutrients applied singly and in combinations varied markedly with soil type. Phosphorus plus Fe and micronutrient combinations containing Fe were most effective and exhibited a synergistic effect on yield of dry matter and DTPA extractable Fe. Soil DTPA extractable Fe was significantly correlated with dry matter yield (r² = 0.81). Phosphorus stimulated root growth and under these experimental conditions enhanced the effect of soil applied Fe.

Key words:

• Dry matter
• plant composition
• micronutrient uptake
• synergistic effects
• DTPA Fe